Turbine control mechanism



Sept. 6,4 1932. I

o. N. BRYANT TURBINE CONTROL MECHANISM Filed 'June 3o, 19304Sheets-Sheet l WITNESS INVENTOR Oz r'o N. Bryan?.

ATTORNEY Sept. 6, 1932. N.l BRYANT 1,876530 TURBINE CONTROL MECHANISMFiled June Z50, 1930 3 Sheets-Sheet 2 55 .siem/a F/BSAT FLUID FIGB.

WIT ss INVENTOR Oz-zjo N. Bryant Sept. 6, 1932. o. N. BRYANT 1,876,530

TURBINE CONTROL MECHANISM Filed June 30, 1930 5 Sheets-Sheet 5 ATTORN EYu annum 15025 52u55 Patented Sept. '6, 1932 Unirse-STATES- ozno N.BRYANT, oF ivroorns, rENNsYnvANIA, AssIGNoR To wEsTINGHoUsE Enno-APATENT orifice.

TRIO & MANUEAGTURINGVCOMPANY, A conronarroivor PENNSYLVANIA v q TURBINEcoNrnoL ivrncirnlvrsifiV 'Application lfiled .Tune :30,

My invention relates to a control mechanism for ar primemovenmoreparticularly Ato a control mechanism for a multistage kelasric fluid'prime mover having -openings at `two or more intermediate pressurestages for extracting partially expanded motive fluid from the primemover or 'for vadmitting motive fluid thereto, and it has for itsob]ectto provide` an improved constructionof suchv mechanism. y I I Amore particular object is Ito provide a control mechanism ofthecharacter set forth which will, upon changein demand for `liow of fluidthrou gh one of the openings, operate the valve means at said oneopening to effect the desired change in flow and 'to maintain thedesired-pressure,and which will at the same time operate the admissionvalve and the valve means at the otheropening to ma1n-'` follmvingdescription and claims taken in l connection with the accompanyingdrawings,

forming a part ofthisapplication, in which: Fig. 1 is a diagrammaticview of lone-embodiment of .the control mechanism applied to amulti-stage elasticfluid turbine; P

Fig-2 is an elevation of a detail; and

3 is a diagrammatic view of amodiied form oit' controlmechanism. i

` Figures 4 to 7 inclusive are diagrammatic illustrations of thegoverning mechanism showing thepositions Voli-the levers for va- ,l

rio-us conditions of bleeder pressure.

Referring `now totheV drawings more A1n` detail, in Fig. 1T, lwshow anelasticluid turbine 10 having a casing 1-1' and .a rotor'12. `The Yturbine is supplied withmotive fluid, which 1930. serial No.' 464,985. i

thereof` to the turbine is Acontrolled by an admission valve 14.1 r

The turbine 10 is designed for operation in connection with demand forelastic fluid at two different pressures belowlthe pressure at `whichmotive fluid is admitted to the turbine.,l For example, elastic iiuid atpressures of V125V lbs. per square inchy and 8 lbs. per square inch mayhe required, while elastic liuid'mav be admitted tothe 'turbine atxapressure of 400 lbs. per square inch.l The expansion from the latterpressure toy either of the lowerpressures is utilized in the tur whichelastic fluid at the higher extractionpressure, may be withdrawn fromthe turbine to a conduit 16.- It is ormedwitha similar fpening 17 at alower, intermediate-pressure stage 17 from which elastic fluid of lowerextraction pressure may bek withdrawn tov a conduit 18. rIfhe openings15 and17 divide the turbine vinto a high-pressurejsection 19, anintermediate pressure section 21anda'lowpressure. section 22, theintermediate pressure stages land 17 receiving partiallyzexpanded-motivefluid from the discharge or lowfpressure ends of thehigh-pressurek section 1-9 and the intermediate. pressure section21,1r'espectively-V y A diaphragm 23 is provided between the pressurestage 15 `and the section 21, and a diaphragm 24 is provi-ded betweenthe'pressure stage 17 andthe section 22. A passage 25 provides aby-p'ass around the diaphragm 23 and contains a valve 26 for controllingthe to control rthe flow of motive iuid to the lowf pressure section 22.

' Itisthe function of the valves 26 and28 to maintain thedesiredpressures at the-pressure stages 15 and 17, and the corresponding'openings 15 and 17, by holding back from the llowerfstages the amountof motive fluid re- .quiredfor extraction. In order to ymaintain vthe4pressures at the extraction stages and the speed of the turbinesubstantially constant, the action of these valves and the admissionvalve 14, upon changes in load and demands for extracted fluid, shouldbe as follows:

Assume first, constant demands and flows at the openings and 17, and achange in load on the turbine; for example, an increase in load. All ofthe valves should be moved Vin opening .direction an amount to provideequal additional flow of motive fluid through all sections of theturbine.

Assuming constant load and constant demand at the opening 17, and anincrease in demand at the opening 15, there shuld be I an increasedopening of the admission valve l14 and decreased openings of thevalves26 and 28. The increased amount of motive fluid heldV back by thevalve 26 and the increased admission by the valve 14 provide theincreased amount of extracted fluid. The valve 28 decreases theadmission to the lowpressure section 22 by an' amount equal to thedecrease in flow through the intermediatepressure section `21, so thatthe amount of fluid for extraction through the opening 17 remains thesaine. A portion or the power development is transferred from theintermeprovide the increased amount of fluid for eX- traction, and aportion of the power development of the low-pressure section 22 istransferred to the high-pressure section 19 and theintermediate-pressure section 21.

1n other words, as the demand for eX- tracted fluid increases at any oneopening, the valves on the high-pressure side thereof should be moved inopening direction, while the valves on the low-pressure side thereofshould be moved in closing direction.

Such operation of the valvesis effected by my novel control mechanismwhich will now be described. rlhe valves 14,V 26 and 28 are connected tofluid pressure governors 29, 31 and '32, respectively. Each governorincludes a cylinder 33, and a piston 34 operating therein and connectedto the associated valve through alever 35 pivoted to a stationaryfulcrum at 36. A spring 37 biases the piston 34 in the direction foropening the associated valve.

Fluid pressure varyin as the' square of the speed of the turbine isdeveloped by an im peller 38 mounted on the rotor shaft 39. It isconveyed through a conduit 41 to the cylinder 33 ofeach governor andimposed on the -the piston and having a slot'53.v

piston 34 in opposition to the spring 37 and in the direction forclosing the associated valve.

It is to be understood that any suitable form of governor may beemployed, and that it may 'embody a fluid pressure relay mechanism. Twoforms of suitable construction are shown in my Patent No. 1,7 78,004,granted October 7, 1930.

In orderv to modify the action of the several governors in accordancewith the variations in demand for extracted fluid, l apply an opposingfluid pressure to the opposite side of the piston 34 of each governor,biasing the pistonin valve-opening direction. This opposing pressure isderived from a. restricted flow,through an orifice 42 which may belocated in the piston 34, ofv fluid under pressure delivered by theimpeller 38. rvlhe vopposing pressures applied to the governors 29, 31and 32 are controlled by pressure relief valves 43, 44 and45,respectively, communieating with the'governors through conduits 46, 47and 48, respectively.

Each pressure relief valve is biased to closed position by aspring 49,whose compression is varied by aV piston 50,operating in a cylinder' 51.The piston 50 is contr. "l d by a stem 52 extending through an opeV .gin The piston 50 is moved to a given position relative to the stem 52 bymeans of a restricted flow of fluid pressure to the cylinder 51,supplied from a branch of the conduit 41 through an orifice 54.

rlhe fluid pressure forces the piston 50 downwardly to compress thespring'49 until lthe slot 53 is uncovered suliiciently by the piston 50to permit escape of the fluid at a rate equal to its admission throughthe orilice 54. Thus, byvertical movement of the stein 52, the piston 50is movedV to vary the pressure or compression of the spring 49 and thevalue of the opposing fluid pressure applied to the piston 34 of theassociated governor. l

A pressure-responsive diaphragm 55, subj ected to the pressure of thefluid in the conduit 16 conveyed through a conduit 56, is

Y pivoted to a lever 57. The latter is pivoted to a stationary fulcrum58 and it is biased in opposition to the force of the pressure onthediaphragm by a group of weights 59 and a spring 61. Y

A secondpressure-responsivediaphragm 62,

subjected to the pressure in the conduit 18 conveyed through aconduit63, is pivoted to a lever 64. 'The latter is pivoted to a stationaryfulcrum and is biased in opposition to *the force of the fluid pressureon the ,dia-f phragm 62 by a group of weights 66 and a spring 67. Thesprings '61 and 67 are ad- ]ustable to provide some adjustment of thepressuresV tofbe maintained in the conduits 16 and 18. i

f the spring.

The lever 57 is pivot'ed at 68 to a float-ing lever 69. 'The 'lever69has three arms, the arms 1 and 72 being connected vto the stems of thepressure reliefvalves 44' and 45, re-

spectively. The third arm 73 is connected by means of a link 74 to anarm 75 carried by the lever 64, the connection being such that movementof the lever 64 rotates the lever 69 about the pivot 68. A. floatinglever 76 is connected at one end to'thelever 64 and atits other end,

through a link 77, to the lever 57. Interme-y `with the extractionpressures remaining constant, providing constant opposing pressures in'the governors. lf tlieload is decreased, the speed increases, andtheincreased impeller pressure acts on the piston 34 of each governor tomove the associated valve in closing direction. 'The flow to eachv ofthe sections 19, 21 and 22 is decreasedby a likev amount, the differencein flow between the l valve 26 and thel additional steam admitted v bythe. admission valve 14 suppliesthe 'ad--, 95

high-pressure section and the intermediatepressure section 21, which issupplied to the opening 15, remaining constant, and the differencebetweenthe flow through the inter- Vvmediate-Uressure section 21 and thelow-pressure section 22, which vis supplied to the opening 17 alsoremaining constant. Upon increase in load, the speed decreases. Theresulting decreased impeller pressure permits the sprng 37 of eachygovernor to move the piston 34 in valve-opening direction'.

the turbine is provided to carry the increased load, the flow throughthe openings 15 and 17 remaining thesame.

Assume .now a condition of constant demand for extracted fluid at thelower extraction pressure, and an -increase in demand for extractedfluid at the higher extraction pressure at the'opening 15, theloadremaining constant. The lever 64 remains stationary. The increase indemand for the higher pressure extracted fluid is accompanied by adecrease in pressure thereof, withinthe limited regulating range, whichydecrease in pressure is communicated through the conduit 56 to thediaphragm 55. The operation may be more readily understood by referenceto Fig; 4, wherein the positions of the levers before the decrease inpressure are indicated in full lines, and by Vdotted lines after thedecrease in pressure. The lever 57 is tilted in counter-cloclrwisedirection by the spring'61 an amount determined by the effective scaleof y 'The upward movementof the right-hand end of the lever 57 raisesthe'lever 69. rlhe upwardimovement ofthe lever 69 is high-pressuresection 19.

l An increase in flow throughout all 'the sections of e'flectedwithoutany appreciable tilting thereof about the pivot 68 by reason of theconnection of` the arm 73 withthe arm 75 through the link 74. Both arms7 land 72 .move upwardly, therefore, moving the stems 52 of the Y 7opressure relief valves 44 and 45 upwardly"v with them. As heretoforeexplained, `upward movement of the stem 52 results in decreased pressureprovided by the reliefvalve, 'and the pressure relief valves 44 and 45dey75 crease the opposing pressures-on top of the V pistons 34 in thegovernors 31 and 32.'y Said pistonsv are thereuponmoved by the impellerpressure amounts' determined by the springs 87 to effect Vclosingmovements ofthe-.valves ,80 26 and-28. i 1 f The upward movement of theright-hand end o-f the lever 57 also results in upward movement of theright-handend of the floatn ing lever 76,'the left-hand end being heldi85 stationaryby the lever 64. The lever 79 is 4 tilted in clockwisedirection, effecting downwardA movement ofthe stem 52 of the pressurerelief vvalve 43. The latter thereupon provides an increased opposing'pressure iii-w90 the governorf29, and the"4 latter moves-'the admissionvalve 14 in openin direction.

The additional steam hel back at the ditional high-pressure extractedfluidto the opening 15. The decreasey in power developmentin'the"interinediate-pressure section 21 and the low-pressure section 22is balanced bythe increase in power development in the The closingmovement of the 'valve 28 effects a decrease in flow .to thelow-pressure section 22 equal to the decrease inflow through the valve26, so

thatthe vamount of extracted fluid supplied 10.5

' to the opening 17 remains constant.

Upon decrease in demand for high-presf surefextracted fluid,\th`epressure thereof increases and the parts of the control mechanism eachmove in the opposite direction. The flow through the high-pressuresection 19 is decreased, and the flow through the intermediate-pressuresection 21 and the lowpressure section 22 is increased.

Assume now an'increase in demand for 115V `T he arm 75 moves the-arm 73to the left, ro-

tating the lever 69 in clockwise direction. lThe lever arm 72 movesupwardly andthe pressure relief valve 45 provides decreased 130 opposingpressure in the governor 32. The latter moves the valve 28 in closingdirection to hold back additional fluid from the low-pressure section22.

The downward movement of the lever arm 71 controls thepressure reliefvalve 44 to `provide'increasedy opposing pressure in the governor 31,and the latte-r effects increased opening of the valve 26.

`The upward movement of the right-hand end of the lever 64 effectsupward movement of the left-hand end of the floating lever 76, theright-hand end being held stationary by the link 77. 'The lever 79 istilted in clock-l wise direction, through the link 78, producingdownwardmovement of the stem 52 of the pressure reliefvalve 48. Thelatter effects increased opposing pressure in the governor 29, which inturn effects increased opening of the admission valve 14.

rlhe increased openings of the valves14 and 26 are such as to provideequal increases in flow through the high-pressure section and theintermediate-pressure section 21. This increased flow, together ywiththe additional steam held back by the valve 28, supplies the increaseddemand for low-pressure extracted fluid. Said increase .in flow is sorelated to the steam held back by the valve 28 that the decrease inpower development bythe lowpressure section 22 is balanced by theincrease in power development by the highpressure section 19 and theintermediatepressure section 21.

Upon decrease in demand for low-pressure extracted fluid, the pressurethereof increases and the rparts move in opposite directions.

rlhe flow through the high-pressure section 19 and theintermediate-pressure section 21 is decreased and the flow through thelowpressure section 22 is increased. The decrease in power developmentby the first two-mentioned sections is balanced by the increase in powerdevelopment by the low-pressure section 22.

lt is to be understood that a simultaneous change in pressure at both ofthe openings and 17 effects a resultant change in the positions of thevarious levers which isexactly the same as if the changes in pressurehad occurred successively, producing first one, and then another of theoperations described above.

The relations of changes in flow effected bv the above-describedoperations are effected by properly proportioning the dimensions of thevalves 14, 26 and 28, the diameters of the pistons 34 and the scales ofthe springs 87 in the governors, the scales of the pressure reliefvalves, thevarious lever arm ratios, the scales of the springs 61 and 67and the diameters of the diaphragms and 62. The

Y determination of these relations involves only mathematicalcalculations and can be determined by one skilled in the art.

In order to adapt the control mechanism so that it may be readilyapplied to various operating conditions, l preferably provide a group orseries of pivot openings in each of the levers 69, 76 and 79 and thelever arm 75. The pivot 68 of the lever 57 is preferably carried by aseparate piece 68 secured to the lever by pins extendingthrough openings57 in the lever 57. ln order to vary the location of the piece 68 on thelever 57, a series of openings 57 is provided.

Suitable forms of adjustment may be ern.- ployed throughout the controlmechanism. For example, as shown in Fig. 2, each stem 52 may beadjustably secured to its lever by a block 88, which is screw threadedon the stem and held in place by a lock nut 89. The block 88 carriespivot pins 91 extending through openings in links 92, which are pivotedat their upper ends to the attached lever,

for example, the lever 79. By turning the stem 52 in the lblock 88, thepressure relief valve may be adjusted to provide any desired pressure,within limits of adjustment, for a given position of the lever;

lt will be apparent that the pressure within the region enclosed by anextraction pressure stage and the opening and extraction conduitcommunicating therewith is substantially the same, or at least variessimilarly with changes in demand,and that the pressure for controllingthe associated pressureresponsive diaphragm may be taken at any .pointwithin that region.

Either or both of the openings 15 and .1.7 may be utilized to admitmotive fluid of suitable pressure to the corresponding staffe instead ofextracting fluid therefrom. The operation of the parts isv exactly thesame, although possibly the pressure setting might be slightly changedby adjusting the initial setting of the corresponding spring 61 or 67.

Assuming, for example,'admissi`on of motive fluid through the opening15, an increasel in supply would be accomplished by an increase inpressure imposed on the diaphragm 55. Such increase in pressure wouldoperate. as above described, to effect increased opening of the valves26 and 28 and decreased opening of the admission valve 14. Theadditional motive fluid admitted through the opening 15 would beutilized in the intermediate pressure 21 and the low-pressure section22, requiring a decreased admission of highpressure motive fluid by theadmission valve 14. A

Likewise, motive fluid Aat a pressure suitable for use in the lowpressure section 22 may be admitted through the opening 17. The controlmechanism operates in the same manner as when fluid is extracted throughthe opening 17, the valve 28 moving in opening direction with increasein supply and Vpressure'of fluid for the low pressure section andthevalves 14and 26 moving in closing direction to maintain the proper load.

Upon decrease in supply `and pressure of fluid admitted through either'vopening 15 7 or 17 the operation is -in the reverse direction.

connected, through links 82E and 88', to ay floating lever 84. Thevpressure relief valve 44 is connected to the lever 84 on the side ofthe link 82 remote from the link 83. The pressure relief valve isconnected-to the lever 84 between the links 82 and 83.

The pressure relief valve 43 is connected to the lever 84 at a pointbetween the links 82 and 83 by means of a link 85 and a lever 86 pivotedto a stationary fulcrum at 87.

The operation of this embodiment in re-` sponse to changes in load andspeed is yas follows: f Y

VAssuming a constant load and constant demand for low-pressure extractedfluid, an increase in pressure on the diaphragm 55., occasioned by adecrease in demand for highpressure extracted fluid, moves the lever 57a in clockwise direction.

positions shown in Fig. 6, the lever *64a remaining stationary-- Thelever 84 is moveddownwardly about the link 83'as a fulcrum. rl`he stems52 of the pressure relief` valves 44 and 45 are moved downwardly toprovide increased opposing fluid pressures in the'governors 31 and 32,ythe latter operating to provide increased opening of the valves 26 and28. The movement of` the lever 84, transmitted throughthe link 85'andthe lever results .in upward movement ofthe 'ste'in,

52 in the pressure relief valve 43. The' latter provides a decreasedopposing pressure in the governor 29, which A effects decreasedopening'of .thej admission valve 1,4.'`

Upon decrease lin pressure on the dia-- phragm 55, the parts operate inthe opposite directionV as Vwill be apparent.

Upon increase in pressure of the low-pressure extracted fluid, thediaphragm 62 moves the lever 640J in clockwise direction. The leversmove from the full line positions to thedotted line positions shown inFig. 7, the lever 57 a remaining stationary. Theflever 84 is tiltedabout the link 82,1the' stem of the pressure relief valve 44 being movedupward- 1n Fig. 3, I show anv'iembodiment of my The levers move from thefull line positions to the dotted liner ly and the stem of the pressurerelief vvalve 45 being moved downwardly. The stem 52 of the pressurerelief valve 43 is also moved upwardly. .The pressure relief valves 43and 44 provide decreased opposing pressures in the governors 29 and 31,resulting in decreased opening of the valves 14 and 26.

The pressure relief valve 45 ,provides increased opposing pressure Yinthe governor 82, resulting in opening movement of the valve 28. The flowthrough the high-pres-V sure and intermediate-pressure sectionsvr isdecreased andthe flow through the'low pressure section is increased,thereby decreasing the flow to the conduit 18 and maintaining the loadon the turbine. Upon decrease in pressure on the diaphragm 55, eachof4the parts moves in the opposite direction.

VIt will be noted that the opposing fluid pressure imposed on eachgovernor of either embodimentis increased in response to in-4 crease inpressure at any opening on the upstream or'high-pressure side of theassociated valve and that itis decreased upon .decrease in pressure atany such opening. The opposing pressure is vdecreased by increasedpressure at any opening on the low-pressure or down-stream side of theassociated valve, and 1t is increased upon decrease inpressure at anysuch opening. v Y

f For the purpose of assisting in reading certain of the claims on thedrawings, the opposing -iuid pressures in the conduits 46,l 47,

vand 48 have been designated first, second, and

third fluid pressures, respectively. It will be note that thev movementsof the pressureresponsive kdiaphragms 55 and 62 are in the samedirection to effect change in a given direction in the Afirst fluidpressure. l For eX- ample, upward movement of the diaphragm 55vinresponse to increase in pressure at the opening 15 effects decrease inthe first fluid pressure, and the movement of the .pressureresponsivediaphragm is the same,that is, up-l ward in responseto increase inpressure at the opening 17, to effect decrease in the rstviluidpressure. The pressure responsiveV diaphragms 55 and 62 movein oppositedirections, that is, onemovesin response to an increase in pressureandthe other moves in responseV to a decrease in pressure, to effectchange in a given direction in the second fluid pressure. Change in agiven direction in thel third fluid pressure is provided by movements ofthe pressure responsive elements in the same direction.`

' While I have shown-my invention in two forms, it will be obvious tothose skilled in theart that itis not so limited, but is susceptiy bleof various other changes and modifications, v withoutl departing fromthe spirit thereof, and I desire, therefore, that only such. limitationsshall be placed thereupon Jas are imposed by the priorart or asarespecifically set forth in the appended claims.

a iso Eil .exterior of theprime mover and a plurality of' intermediatepressure stages and a valve means controlling the flow of motive fluidat each of said intermediate lressure stages, of a regulating mechanismfor each of said lastmentioned valve means comprising means providing afluid pressure varying in consequence of variations in demand for flowthrough eitherv of the communicating means and means responsive to saidfluid pressure for controlling the vvalve means.

2. The combination with a multistage prime mover having admission valvemeans, openings communicating with a plurality of intermediate pressurestages, respectively, and the outside of the `prime mover, a valve meanscontrolling the flow of motive fluid at each of said intermediatepressure stages, of a regulating mechanism for each of saidlast-mentioned valve means comprising means providing a fluid pressurevarying in response to variations in pressure in either of saidopenings, and means responsive to said fluid pressure for controllingthe valve means.

3. The combination with a multi-stage prime mover having admission valvemeans, means providing communication between the exterior of the primemover and aplurality o'fintermediate pressure stages and a valve' meanscontrolling the flow of' motive fluid at each of said intermediatepressure stages, of a regulating mechanism for each of the valve meansincluding a'pressure-responsive controlling element and means forapplying to the pressure-responsive controlling element a fluid pressurevarying in consequence of variations in demand for flow through each ofthe communicating means.

4. The combination with a multistage prime mover having admission valvemeans, openings communicating with a plurality of intermediate pressurestages, respectively, a valvemeanscontrolling the flow ofrmotive fluidat each of said intermediate pressure stages, of a regulating mechanismfor each of the valve means including a pressure responsive controllingelement, and means for applying to the pressure responsive controllingelement a fluid pressure varying in response to variations in pressurein each of said openings.

5. The combination with a multi-stage elastic fluid prime mover havingopenings communicating respectively with a plurality of pressure stagestherein, valve lmeans controlling the admission of motive fluid to theprime mover and a valve means controlling the flow of fluid at eachofsaid openings, of means associated with each of the valve means forregulating-the samev comprising means providing a fluid pressure whichvaiger/assai ries in one direction in response toincrease in pressure atan opening on the high-pressure side of the valve means and decrease inpressure at. an opening on the low-pressure side of the valve means andwhich varies in the opposite direction in response to decrease inpressure at an opening on the high-pressure side of the valve meansandyincrease in pressure at an opening on the low-pressure side of thevalve means, and means responsive to said fluid pressure for controllingthe valve means.

6. The combination with an elastic fluid prime mover having ahigh-pressure section,

an intermediate-pressure section,'a low-pressure section, and an openingbetween the high-pressure and intermediate-pres-sure sections and anopening between the intermediate-pressure and low-pressure sections foradmitting or discharging motive fluid, of means providing a fluidpressure which varies in one direction in response to increase inpressure of motive fluid at the first-mentioned opening andin theopposite direction in responsetoincrease'in pressure at thesecond-mentioned opening, means responsive to said fluid pressure forcontrolling the flow of motive fluid to the intermechate-pressuresection, means providing a second fluid pre-ssure which varies in onedirection in response tovincrease in pressure of motive fluid at thefirst-mentioned opening and in the same directiony in response toincrease in pressure at the second-mentioned opening, and meansresponsive to said second fluid pressure for controlling the flow ofmotive fluid to the low-pressure section.

7. The combination with a prime mover having a high-pressure sec'tion,an intermediate pressure section, a low-pressure section, a firstopening between the high-pressure and intermediate-pressure sections anda second opening between the intermediate-pressure and low-pressuresections for admitting or discharging motive fluid, of means providing afirst, a second, and a third fluid pressure each varying in response tothe changes in pressure at said openings, the changes in pressure atsaid openings being in thesame direction, relative to each other, forproviding variation in a given direction in the firstV fluid pressure,in the opposite direction, relative to each other, for providingvariation in a given direction in the second fluid pressure, and in thesame direction, relative to each other, for providing variation in agiven direction in the third fluid pressure, and means for controllingthe flow of fluid to the high-pressure section, the intermediatepressure section and the low-pressure section in response to the first,the second, and the third fluid pressure, respectively. n

, 8. The combination with a multi-stage elastic fluid prime mover havingopenings communicating with two pressure stages IBO therein,respectively, and the outside of the prime mover, valve meanscontrolling the admission to the prime mover and a valve meanscontrolling the flow ofV fluid at each of said openings, of a controlmechanism comprising two pressure-responsive elements each subjected tothe pressure at one of said openings, means controlled by saidpressureresponsive elements for providing a first, a second, and a thirdiuid pressure, the. movements of the pressure-responsive elements beingin the same direction, withrespect to each other, to provide a change ina given direction of the first fluid pressure, the move? ments of thepressure-responsive elements being in the opposite direction, withrespect to each other, to provide a change in a given direction in thesecond fluid pressure, the movements of the pressure-responsivelelements being in the same direction, with respect to each other, toprovide a change in a given direction in the third fluid pressure, andmeans for operating the admission valve means, the valve means at thestage of higher pressure and the valve means at the ystage of lowerpressure in response to the first, the second and the third fluidpressure, respectively. V

9. The combination dened in claim 8 and further comprisingmeansproviding a fluid pressure varying as a function of the speed ofthe prime mover and wherein the valve means are also operated inrespon-se to said last-mentioned fluid pressure.

In testimony whereof, I have hereunto subscribed my name this 26th dayof J une, 1930.

OZRO N. BRYANT.

